Albert W. Florence believes that black men who drive nice cars in New Jersey run a risk of being questioned by the police. For that reason, he kept handy a 2003 document showing he had paid a court-imposed fine stemming from a traffic offense, just in case.

It did not seem to help.

In March 2005, Mr. Florence was in the passenger seat of his BMW when a state trooper pulled it over for speeding. His wife, April, was driving. His 4-year-old son, Shamar, was in the back.